Lithographic apparatus, cover for use in a lithographic apparatus and method for designing a cover for use in a lithographic apparatus

ABSTRACT

A lithographic apparatus having a fluid handling structure configured to contain immersion fluid in a space adjacent to an upper surface of a substrate table and/or a substrate located in a recess of the substrate table, a cover including a planar main body that, in use, extends around a substrate from the upper surface to a peripheral section of an upper major face of the substrate in order to cover a gap between an edge of the recess and an edge of the substrate, and an immersion fluid film disruptor configured to disrupt the formation of a film of immersion fluid between an edge of the cover and immersion fluid contained by the fluid handling structure during movement of the substrate table relative to the fluid handling structure.

This application is a continuation of U.S. patent application Ser. No.13/047,165, filed Mar. 14, 2011, which claims priority and benefit under35 U.S.C. § 119(e) to U.S. Provisional Patent Application No.61/314,266, entitled “Cover For A Substrate Table, Substrate Table For ALithographic Apparatus, Lithographic Apparatus, and Device ManufacturingMethod”, filed on Mar. 16, 2010, to U.S. Provisional Patent ApplicationNo. 61/346,213, entitled “Lithographic Apparatus, Cover For Use In ALithographic Apparatus and Fluid Handling Structure For Use In ALithographic Apparatus”, filed on May 19, 2010, and to U.S. ProvisionalPatent Application No. 61/388,923, entitled “Lithographic Apparatus,Cover For Use In A Lithographic Apparatus and Method For Designing ACover For Use In A Lithographic Apparatus”, filed on Oct. 1, 2010. Thecontents of each of the foregoing applications is incorporated herein inits entirety by reference.

FIELD

The present invention relates to a lithographic apparatus, cover for usein a lithographic apparatus and a method for designing a cover for usein a lithographic apparatus.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. In an embodiment, the liquid isdistilled water, although another liquid can be used. An embodiment ofthe present invention will be described with reference to liquid.However, another liquid may be suitable, particularly a wetting fluid,an incompressible fluid and/or a fluid with higher refractive index thanair, desirably a higher refractive index than water. Fluids excludinggases are particularly desirable. The point of this is to enable imagingof smaller features since the exposure radiation will have a shorterwavelength in the liquid. (The effect of the liquid may also be regardedas increasing the effective numerical aperture (NA) of the system andalso increasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein, or a liquid with a nano-particle suspension (e.g. particleswith a maximum dimension of up to 10 nm). The suspended particles may ormay not have a similar or the same refractive index as the liquid inwhich they are suspended. Other liquids which may be suitable include ahydrocarbon, such as an aromatic, a fluorohydrocarbon, and/or an aqueoussolution.

Submersing the substrate or substrate and substrate table in a bath ofliquid (see, for example, U.S. Pat. No. 4,509,852) means that there is alarge body of liquid that should be accelerated during a scanningexposure. This may require additional or more powerful motors andturbulence in the liquid may lead to undesirable and unpredictableeffects.

Other arrangements which have been proposed include a confined immersionsystem and an all wet immersion system. In a confined immersion system aliquid supply system provides liquid on only a localized area of thesubstrate and in between the final element of the projection system andthe substrate using a liquid confinement system (the substrate generallyhas a larger surface area than the final element of the projectionsystem). One way which has been proposed to arrange for this isdisclosed in PCT patent application publication no. WO 99/49504.

In an all wet immersion system, as disclosed in PCT patent applicationpublication WO 2005/064405 the immersion liquid is unconfined. In such asystem the whole top surface of the substrate is covered in liquid. Thismay be advantageous because then the whole top surface of the substrateis exposed to the substantially same conditions. This may have anadvantage for temperature control and processing of the substrate. In WO2005/064405, a liquid supply system provides liquid to the gap betweenthe final element of the projection system and the substrate. Liquid isallowed to leak over the remainder of the substrate. A barrier at theedge of a substrate table prevents the liquid from escaping so that itcan be removed from the top surface of the substrate table in acontrolled way.

The immersion system may be a fluid handling system or apparatus. In animmersion system, immersion fluid is handled by a fluid handling system,structure or apparatus. In an embodiment the fluid handling system maysupply immersion fluid and therefore be a fluid supply system. In anembodiment the fluid handling system may at least partly confineimmersion fluid and thereby be a fluid confinement system. In anembodiment the fluid handling system may provide a barrier to immersionfluid and thereby be a barrier member, such as a fluid confinementstructure. In an embodiment the fluid handling system may create or usea flow of gas, for example to help in controlling the flow and/or theposition of the immersion fluid. The flow of gas may form a seal toconfine the immersion fluid so the fluid handling structure may bereferred to as a seal member; such a seal member may be a fluidconfinement structure. The fluid handling system may be located betweenthe projection system and the substrate table. In an embodiment,immersion liquid is used as the immersion fluid. In that case the fluidhandling system may be a liquid handling system. In reference to theaforementioned description, reference in this paragraph to a featuredefined with respect to fluid may be understood to include a featuredefined with respect to liquid.

In a fluid handling system or liquid confinement structure, liquid isconfined to a space, for example within a confinement structure. Thespace may be defined by the body of the confinement structure, theunderlying surface (e.g. a substrate table, a substrate supported on thesubstrate table, a shutter member and/or a measurement table) and, inthe case of a localized area immersion system, a liquid meniscus betweenthe fluid handling system or liquid confinement structure and theunderlying structure i.e. in an immersion space. In the case of an allwet system, liquid is allowed to flow out of the immersion space ontothe top surface of the substrate and/or substrate table.

In European patent application publication no. EP 1420300 and UnitedStates patent application publication no. US 2004-0136494, each herebyincorporated in their entirety by reference, the idea of a twin or dualstage immersion lithography apparatus is disclosed. Such an apparatus isprovided with two tables for supporting a substrate. Levelingmeasurements are carried out with a table at a first position, withoutimmersion liquid, and exposure is carried out with a table at a secondposition, where immersion liquid is present. Alternatively, theapparatus has only one table.

After exposure of a substrate in an immersion lithographic apparatus,the substrate table is moved away from its exposure position to aposition in which the substrate may be removed and replaced by adifferent substrate. This is known as substrate swap, In a two stagelithographic apparatus, for example ASML's “Twinscan” lithographicapparatus, the substrate tables swap takes place under the projectionsystem.

SUMMARY

In a lithographic apparatus, a substrate is supported on a substratetable by a substrate holder. The substrate holder may be located in arecess of the substrate table. The recess may be dimensioned so thatwhen a substrate is supported by the substrate holder the top surface ofthe substrate is generally in the same plane as the surface of thesubstrate table surrounding the substrate. Around the substrate, theremay be a gap between an edge of a substrate and an edge of the substratetable. Such a gap may be undesirable in an immersion system of alithographic apparatus. As the gap moves under the immersion liquid inthe space between the final element of the projection system and theunderlying surface, the meniscus between the confinement structure andthe underlying surface crosses the gap. Crossing the gap may increasethe instability of the meniscus. The stability of the meniscus maydecrease with increased relative speed, e.g. scanning or stepping speed,between the confinement structure and the substrate table. Anincreasingly unstable meniscus is a risk to increased defectivity. Forexample an unstable meniscus may enclose gas as a bubble in theimmersion liquid, or may cause a droplet to escape from the immersionspace. Such a bubble may be drawn into the space and result in imagingdefects. A droplet may be a source of contaminants and a heat load as itevaporates and it may later collide with the meniscus causing a bubbleto be drawn in to the space.

One or more problems of crossing the gap may be reduced by the provisionof a two-phase extraction system. The two phase extraction systemextracts fluid such as immersion liquid and gas (which may be present asa bubble in the liquid) from the gap. Sources of defectivity, such asreleasing a bubble into the space or a droplet escaping from the space,may be reduced if not eliminated. However, the provision of such anextraction system may impart a heat load on the substrate table and thesubstrate. This may have a negative impact on the overlay accuracy ofpatterns formed on the substrate. The gap may implicitly limit the scanspeed that may be used to achieve reliable imaging of a substrate.

It is therefore desirable to provide, for example, a system to increasethe stability of the meniscus and reduce defectivity, for example thelikelihood of creating a bubble or releasing a droplet.

In an aspect of an invention, there is provided a lithographic apparatuscomprising:

a substrate table having an upper surface and a recess in the uppersurface that is configured to receive and support a substrate;

-   -   a fluid handling structure configured to contain immersion fluid        in a space adjacent to the upper surface of the substrate table        and/or a substrate located in the recess;    -   a cover comprising a planar main body that, in use, extends        around a substrate from the upper surface to a peripheral        section of an upper major face of the substrate in order to        cover a gap between an edge of the recess and an edge of the        substrate; and    -   an immersion fluid film disruptor, configured to disrupt the        formation of a film of immersion fluid between an edge of the        cover and immersion fluid contained by the fluid handling        structure during movement of the substrate table relative to the        fluid handling structure.

In an aspect of an invention, there is provided a method of designing acover for use in an immersion lithographic apparatus that includes asubstrate table having a substantially planar upper surface in which isformed a recess that is configured to receive and support a substrate,the cover comprising a substantially planar main body that, in use,extends around the substrate from the upper surface to a peripheralsection of an upper major face of the substrate in order to cover a gapbetween an edge of the recess and an edge of the substrate; wherein anedge of the cover is tapered such that the thickness of the covergradually decreases across the edge, the method comprising selecting theangle of the surface of the section of the cover that is tapered,relative to the upper major face of the substrate, in order that thesection of the cover in use disrupts the formation of a film ofimmersion fluid between the edge of the cover and immersion fluidcontained by a fluid handling structure of the lithographic apparatusduring movement of the substrate table relative to the fluid handlingstructure.

In an aspect of an invention, there is provided a method ofmanufacturing a cover using the above method of designing a cover and acover manufactured thereby.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a fluid handling structure as a liquid supplysystem for use in a lithographic projection apparatus;

FIG. 4 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts, in cross-section, a liquid confinement structure whichmay be used in an embodiment of the present invention as a liquid supplysystem;

FIG. 6 depicts, in plan view, a substrate receiving section according toan aspect of the invention;

FIGS. 7 and 8 depict, in plan view, a cover according to an aspect ofthe invention in open and closed positions, respectively;

FIGS. 9 and 10 depict, in plan view, a cover according to an aspect ofthe invention in closed and open positions, respectively;

FIGS. 11, 12 and 13 depict, in cross-section, an actuator system for acover according to an aspect of the invention in, respectively, theclosed position, an intermediate position and the open position;

FIGS. 14 and 15 depict, in cross-section, an arrangement of movementguides that may be used in an actuator system of an aspect of theinvention;

FIGS. 16, 17 and 18 depict an actuator system for a cover according toan aspect of the invention in, respectively, a closed position, anintermediate position and an open position;

FIGS. 19 and 20 depict, in cross-section, a cover according to an aspectof the invention;

FIG. 21 depicts, in cross-section, an arrangement of a cover accordingto an aspect of the invention;

FIGS. 22 to 25 schematically depict possible configurations of the edgeof a cover according to an aspect of the invention;

FIGS. 26 to 32 schematically depict, in cross section, arrangements ofcovers according to an aspect of the invention;

FIG. 33 depicts an arrangement of a cover in use;

FIG. 34 depicts an arrangement of a cover in a system including animmersion fluid film disruptor according to an aspect of the invention;

FIG. 35 depicts an arrangement of a cover in a system including animmersion fluid film disruptor according to an aspect of the invention;

FIG. 36 depicts an arrangement of a cover in a system including animmersion fluid film disruptor according to an aspect of the invention;

FIG. 37 illustratively depicts the position of a meniscus crossing theedge of a cover;

FIG. 38 illustratively depicts the position of a meniscus crossing acover under a specific set of conditions; and

FIG. 39 depicts an arrangement of a cover in a system including animmersion fluid film disruptor according to an aspect of the invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL configured to condition        a radiation beam B (e.g. UV radiation or DUV radiation);    -   a support structure (e.g. a mask table) MT constructed to        support a patterning device (e.g. a mask) MA and connected to a        first positioner PM configured to accurately position the        patterning device MA in accordance with certain parameters;    -   a substrate table (e.g. a wafer table) WT constructed to hold a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner PW configured to accurately position the        substrate W in accordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PSconfigured to project a pattern imparted to the radiation beam B bypatterning device MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illumination system IL may include various types of opticalcomponents, such as refractive, reflective, magnetic, electromagnetic,electrostatic or other types of optical components, or any combinationthereof, for directing, shaping, or controlling radiation.

The support structure MT holds the patterning device MA. The supportstructure MT holds the patterning device MA in a manner that depends onthe orientation of the patterning device MA, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure MT can use mechanical, vacuum, electrostatic orother clamping techniques to hold the patterning device. The supportstructure MT may be a frame or a table, for example, which may be fixedor movable as desired. The support structure MT may ensure that thepatterning device MA is at a desired position, for example with respectto the projection system PS. Any use of the terms “reticle” or “mask”herein may be considered synonymous with the more general term“patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system. The types of projectionsystem may include: refractive, reflective, catadioptric, magnetic,electromagnetic and electrostatic optical systems, or any combinationthereof. The selection or combination of the projection system is asappropriate for the exposure radiation being used, or for other factorssuch as the use of an immersion liquid or the use of a vacuum. Any useof the term “projection lens” herein may be considered as synonymouswith the more general term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more patterning device tables). Insuch “multiple stage” machines the additional tables may be used inparallel, or preparatory steps may be carried out on one or more tableswhile one or more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source SO and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source SO is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source SO may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as a-outer anda-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator IL can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator IL may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section. Similar to the source SO, the illuminator IL may or maynot be considered to form part of the lithographic apparatus. Forexample, the illuminator IL may be an integral part of the lithographicapparatus or may be a separate entity from the lithographic apparatus.In the latter case, the lithographic apparatus may be configured toallow the illuminator IL to be mounted thereon. Optionally, theilluminator IL is detachable and may be separately provided (forexample, by the lithographic apparatus manufacturer or anothersupplier).

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device MA. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS.The projection system PS focuses the beam B onto a target portion C ofthe substrate W. With the aid of the second positioner PW and positionsensor IF (e.g. an interferometric device, linear encoder or capacitivesensor), the substrate table WT can be moved accurately, e.g. so as toposition different target portions C in the path of the radiation beamB. Similarly, the first positioner PM and another position sensor (whichis not explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam B is projected onto a target portion C at one time (i.e.a single static exposure). The substrate table WT is then shifted in theX and/or Y direction so that a different target portion C can beexposed. In step mode, the maximum size of the exposure field limits thesize of the target portion C imaged in a single static exposure.

In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam Bis projected onto a target portion C (i.e. a single dynamic exposure).The velocity and direction of the substrate table WT relative to thesupport structure MT may be determined by the (de-)magnification andimage reversal characteristics of the projection system PS. In scanmode, the maximum size of the exposure field limits the width (in thenon-scanning direction) of the target portion C in a single dynamicexposure, whereas the length of the scanning motion determines theheight (in the scanning direction) of the target portion C.

In another mode, the support structure MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the radiation beam B isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as desired after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

An arrangement to provide liquid between a final element of theprojection system PS and the substrate is the so called localizedimmersion system IH. In this system a liquid handling system is used inwhich liquid is only provided to a localized area of the substrate. Thespace filled by liquid is smaller in plan than the top surface of thesubstrate and the area filled with liquid remains substantiallystationary relative to the projection system PS while the substrate Wmoves underneath that area. Four different types of localized liquidsupply systems are illustrated in FIGS. 2-5.

As illustrated in FIGS. 2 and 3, liquid is supplied by at least oneinlet onto the substrate, preferably along the direction of movement ofthe substrate relative to the final element. Liquid is removed by atleast one outlet after having passed under the projection system. Thatis, as the substrate is scanned beneath the element in a −X direction,liquid is supplied at the +X side of the element and taken up at the −Xside. FIG. 2 shows the arrangement schematically in which liquid issupplied via inlet and is taken up on the other side of the element byoutlet which is connected to a low pressure source. In the illustrationof FIG. 2 the liquid is supplied along the direction of movement of thesubstrate relative to the final element, though this does not need to bethe case. Various orientations and numbers of in- and out-letspositioned around the final element are possible; one example isillustrated in FIG. 3 in which four sets of an inlet with an outlet oneither side are provided in a regular pattern around the final element.Arrows in liquid supply and liquid recovery devices indicate thedirection of liquid flow.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets oneither side of the projection system PS and is removed by a plurality ofdiscrete outlets arranged radially outwardly of the inlets. The inletscan be arranged in a plate with a hole in its centre and through whichthe projection beam is projected. Liquid is supplied by one groove inleton one side of the projection system PS and removed by a plurality ofdiscrete outlets on the other side of the projection system PS, causinga flow of a thin film of liquid between the projection system PS and thesubstrate W. The choice of which combination of inlet and outlets to usecan depend on the direction of movement of the substrate W (the othercombination of inlet and outlets being inactive). In the cross-sectionalview of FIG. 4, arrows illustrate the direction of liquid flow in inletsand out of outlets.

Another arrangement which has been proposed is to provide the liquidsupply system with a liquid confinement member which extends along atleast a part of a boundary of the space between the final element of theprojection system and the substrate table. Such an arrangement isillustrated in FIG. 5. The liquid confinement member is substantiallystationary relative to the projection system in the XY plane thoughthere may be some relative movement in the Z direction (in the directionof the optical axis). A seal is formed between the liquid confinementand the surface of the substrate. In an embodiment, a seal is formedbetween the liquid confinement structure and the surface of thesubstrate and may be a contactless seal such as a gas seal. Such asystem is disclosed in United States patent application publication no.US 2004-0207824, hereby incorporated in its entirety by reference.

FIG. 5 schematically depicts a localized liquid supply system with aliquid confinement structure 12. The liquid confinement structure 12extends along at least a part of a boundary of the space 11 between thefinal element of the projection system PS and the substrate table WT orsubstrate W. (Please note that reference in the following text tosurface of the substrate W also refers in addition or in the alternativeto a surface of the substrate table WT, unless expressly statedotherwise.) The liquid confinement structure 12 is substantiallystationary relative to the projection system PS in the XY plane thoughthere may be some relative movement in the Z direction (in the directionof the optical axis). In an embodiment, a seal is formed between theliquid confinement structure 12 and the surface of the substrate W andmay be a contactless seal such as fluid seal, desirably a gas seal.

The liquid confinement structure 12 at least partly contains liquid inthe immersion space 11 between a final element of the projection systemPS and the substrate W. A contactless seal 16 to the substrate W may beformed around the image field of the projection system PS so that liquidis confined within the space 11 between the substrate W surface and thefinal element of the projection system PS. The immersion space 11 is atleast partly formed by the liquid confinement structure 12 positionedbelow and surrounding the final element of the projection system PS.Liquid is brought into the space 11 below the projection system PS andwithin the liquid confinement structure 12 by liquid inlet 13. Theliquid may be removed by liquid outlet 13. The liquid confinementstructure 12 may extend a little above the final element of theprojection system PS. The liquid level rises above the final element sothat a buffer of liquid is provided. In an embodiment, the liquidconfinement structure 12 has an inner periphery that at the upper endclosely conforms to the shape of the projection system PS or the finalelement thereof and may, e.g., be round. At the bottom, the innerperiphery closely conforms to the shape of the image field, e.g.,rectangular, though this need not be the case.

In an embodiment, the liquid is contained in the immersion space 11 by agas seal 16 which, during use, is formed between the bottom of theliquid confinement structure 12 and the surface of the substrate W.Other types of seal are possible, as is no seal (for example in an allwet embodiment) or a seal achieved by capillary forces between theundersurface of the liquid confinement structure 12 and a facingsurface, such as the surface of a substrate W, a substrate table WT or acombination of both.

The gas seal 16 is formed by gas, e.g. air or synthetic air but, in anembodiment, N₂ or another inert gas. The gas in the gas seal 16 isprovided under pressure via inlet 15 to the gap between liquidconfinement structure 12 and substrate W. The gas is extracted viaoutlet 14. The overpressure on the gas inlet 15, vacuum level on theoutlet 14 and geometry of the gap are arranged so that there is ahigh-velocity gas flow inwardly that confines the liquid. The force ofthe gas on the liquid between the liquid confinement structure 12 andthe substrate W contains the liquid in an immersion space 11. Theinlets/outlets may be annular grooves which surround the space 11. Theannular grooves may be continuous or discontinuous. The flow of gas iseffective to contain the liquid in the space 11. Such a system isdisclosed in United States patent application publication no. US2004-0207824.

Other arrangements are possible and, as will be clear from thedescription below, an embodiment of the present invention may use anytype of localized immersion system.

In a localized immersion system a seal is formed between a part of theliquid confinement structure and an underlying surface, such as asurface of a substrate W and/or substrate table WT. The seal may bedefined by a meniscus of liquid between the liquid confinement structureand the underlying surface. Relative movement between the underlyingsurface and the liquid confinement structure may lead to breakdown ofthe seal, for example the meniscus, above a critical speed. Above thecritical speed, the seal may break down allowing liquid, e.g. in theform of a droplet, to escape from the liquid confinement structure, orgas, i.e. in the form of a bubble, to be enclosed in the immersionliquid within the immersion space.

A droplet may be a source of defectivity. The droplet may apply athermal load on the surface which it is located as it evaporates. Thedroplet may be a source of contamination, in leaving a drying stainafter it has evaporated. If the droplet lies in the path on theunderlying surface which moves under the projection system, the dropletmay contact the meniscus. The resulting collision between the meniscusand the droplet may cause a bubble to form in the liquid. A bubble maybe a source of defectivity. A bubble in the immersion liquid may bedrawn in to the space between the projection system and the substratewhere it may interfere with an imaging projection beam.

Critical speed may be determined by the properties of the underlyingsurface. The critical speed of a gap relative to the confinementstructure may be less than the critical speed for the surface of arelatively planar surface such as a substrate. On increasing the scanvelocity above the lowest critical speed for a part of the undersurface,the scan velocity will exceed the critical speed for more of theunderlying surface. The problem may be more significant at high scanvelocities. However, an increased scan velocity is desirable becausethroughput increases.

FIG. 6 depicts, in plan view, a substrate table WT that may be used tosupport a substrate W. The substrate table may have a substantiallyplanar upper surface 21. In the upper surface 21 is a recess 22 that isconfigured to receive and support a substrate W.

In the recess may be a substrate support which may be a surface of therecess, The surface of the recess 22 may include a plurality ofprotrusions on which a lower surface of the substrate is supported. Thesurface of the recess may include a barrier. In the surface of therecess may be formed a plurality of openings. The barrier surrounds theprotrusions to define a space beneath the lower surface of the substrateW. The openings are connected to an under-pressure source. When asubstrate is located above the openings a space is formed beneath thesubstrate W. The space may be evacuated by operation of theunderpressure. This arrangement may be used in order to secure thesubstrate W to the substrate table WT.

In an arrangement, the recess may be configured such that the majorfaces of the substrate, namely the upper face and the lower face, aresubstantially parallel to the upper surface 21 of the substrate table.In an arrangement, the upper face of the substrate W may be arranged tobe substantially coplanar with upper surface 21 of the substrate table.

It should be appreciated that in the present application, terms such asupper and lower may be used in order to define the relative positions ofcomponents within the systems described. However, these terms are usedfor convenience in order to describe the relative positions of thecomponents when the apparatus is used at a particular orientation. Theyare not intended to specify the orientation in which the apparatus maybe used.

As depicted in FIG. 6, a gap 23 may be present between an edge of thesubstrate W and an edge of the recess 22. According to an aspect of theinvention, a cover 25 is provided that extends around the substrate W.The cover 25 extends from a peripheral section of the upper surface ofthe substrate W (which in an embodiment may be an edge of the substrate)to the upper surface 21 of the substrate table WT. The cover 25 mayentirely cover the gap 23 between the edge of the substrate W and theedge of the recess 22. In addition, an open central section 26 of thecover 25 may be defined by an inner edge of the cover. The open centralsection 26 may be arranged such that, in use, the cover 25 does notcover portions of the substrate W on which it is intended to project apatterned beam of radiation. The inner edge of the cover may coverportions of the substrate which neighbor the surface of the substratewhich is imaged by the patterned projection beam. The cover is locatedaway from those portions of the substrate which are exposed by thepatterned projection beam.

As shown in FIG. 6, when the cover 25 is placed on the substrate W, thesize of the open central section 26 may be slightly smaller than thesize of the upper surface of the substrate W. As shown in FIG. 6, if thesubstrate W is circular in shape, the cover 25 may be generally annularin shape when viewed in plan view.

The cover 25 may be in the form of a thin cover plate. The cover platemay, for example, be formed from stainless steel. Other material may beused. The cover plate may be coated with Lipocer coating of the typeoffered by Plasma Electronic GmbH. Lipocer is a coating which may belyophobic (e.g. hydrophobic) and is relatively resistant to damage fromexposure to radiation and immersion liquid (which may be highlycorrosive). More information on Lipocer may be found in U.S. PatentApplication Publication No US 2009/0206304, which is hereby incorporatedby reference in its entirety.

As schematically depicted in FIG. 21, a lyophobic coating 141, such as alayer of Lipocer, may be applied to the lower surface 25 a of the cover25, namely the surface, that in use, may extend from a peripheralsection of the upper surface of the substrate W to the upper surface 21of the substrate table WT. The provision of such a coating 141 on thelower surface 25 a may minimize or reduce the leakage of immersionliquid below the cover 25. For example, the coating 141 may reduce theleakage of immersion liquid between the cover 25 and the upper surfaceof the substrate W. Minimizing or reducing such immersion liquid leakagemay in turn reduce the likelihood of immersion liquid being passed tothe underside of the substrate W. This may reduce defects that may beintroduced as a result of the so-called back side contamination,Minimizing or reducing immersion liquid leakage may reduce a thermalload on the substrate W.

The coating 141 on the lower surface 25 a of the cover 25 may beselected to be an anti-sticking layer. In other words, the coating 141may be selected to prevent, minimize or reduce adhesion of the cover 25to the upper surface of the substrate W and/or the upper surface 21 ofthe substrate table WT. This may prevent or reduce damage to the cover25, the substrate W and/or the substrate table WT when the cover 25 isremoved from the substrate W and the substrate table WT.

The use of a coating 141 on the lower surface 25 a of the cover 25 thatis lyophobic and/or anti-sticking may prevent or reduce the accumulationof contamination particles on the lower surface of the cover 25. Suchcontaminant particles could result in damage to any of the cover 25, thesubstrate W and/or the substrate table WT or provide a source ofsubsequent defects on the substrate W. Alternatively or additionally,such contaminant particles may prevent a sufficient seal being formedbetween the cover 25 and the upper surface of the substrate W and/or theupper surface 21 of the substrate table WT, resulting in leakage of theimmersion liquid, which may be undesirable. Accordingly, it may bedesirable to prevent the accumulation of such contaminant particles.

The lower surface 25 a of the cover 25 and/or the lower surface 141 a ofa coating 141 applied to the lower surface 25 a of the cover 25 may beconfigured to have low surface roughness. For example, for a spraycoating, the surface roughness R_(A) may be less than 1 μm. For adeposited coating the surface roughness R_(A) may be less than 200 nm.In general, reducing the surface roughness of the lower surface 25 a ofthe cover and/or the lower surface 141 a of a coating 141 applied to thelower surface 25 a of the cover 25 may reduce stress concentrations onthe surface of the substrate W. The surface roughness R_(A) of parts ofthe cover 25 in contact with the substrate in use may desirably be lessthan 200 nm, desirably less than 50 nm, or desirably less than 10 nm.

Ensuring that the surface roughness of the lower surface 25 a of thecover 25 and/or the lower surface 141 a of a coating 141 applied to thelower surface 25 a of the cover 25 is low may also assist in reducing orminimizing leakage of immersion liquid below the cover 25. The cover 25may be arranged such that the flatness of the lower surface 25 a of thecover 25 and/or the lower surface 141 a of a coating 141 applied to thelower surface 25 a of the cover 25 is maximized. This may provideoptimized contact between the cover 25 and the substrate W and/or thesubstrate table WT, reducing or minimizing immersion liquid leakage.

As schematically depicted in FIG. 21, a coating 142 may alternatively oradditionally be provided on the upper surface 25 b of the cover 25. Theupper surface 25 b of the cover 25 or the upper surface 142 b of acoating 142 on the upper surface 25 b of the cover may be selected forsmoothness. This may reduce the likelihood of the meniscus being pinned.For example, the upper surface 25 b of the cover 25 or the upper surface142 b of a coating 142 on the upper surface 25 b of the cover may besmooth such that the peak to valley distance of the surface is less than10 μm, desirably less than 5 μm.

The coating 142 on the upper surface 25 b of the cover 25 may beselected to be resistant to damage from exposure to radiation andimmersion liquid. This may help ensure that the working life of thecover is sufficiently long to prevent unnecessary costs associated withreplacing the cover 25, including downtime for the lithographicapparatus. The coating 142 on the upper surface 25 b of the cover 25 maybe selected to be lyophobic, as discussed above. Such a coating mayprovide a higher receding contact angle for the immersion liquid. Thisin turn may permit a higher scan speed to be used without, for example,the loss of immersion liquid from the meniscus, as discussed above. Asnoted above, the coating 142 on the upper surface 25 b of the cover 25may be formed from Lipocer.

It should be appreciated that the coatings 141, 142 on the lower andupper surface 25 a, 25 b of the cover 25 may be formed from the singlelayer of material. Alternatively, one or both of the coatings 141, 142may be formed from a plurality of layers. For example, the layers may beformed from different materials, providing different benefits to thecoating 141, 142. It should also be appreciated that the coatings 141,142 on the lower and upper surfaces 25 a, 25 b of the cover 25 may bethe same or different from each other.

The cover plate may, for example, be 25 μm thick. It may be etched to belocally reduced in thickness, for example at one or more of the edges.In a locally reduced area it may be 10 μm thick. The thickness of partof the cover may be reduced by other processes such as laser ablation,milling and polishing.

As depicted in FIG. 21, the edges 25 c, 25 d of the cover 25, namely theedges separating the lower and upper surfaces 25 a, 25 b of the cover 25may be substantially perpendicular to the lower and upper surfaces 25 a,25 b of the cover 25. Such an arrangement may be relatively simple tomanufacture.

However, in an arrangement as depicted in FIG. 21, the edges 25 c, 25 dof the cover 25 may form a step on the surface of the substrate W andthe upper surface 21 of the substrate table WT. Such a step may beundesirable. In particular, as discussed above, when the substrate W andsubstrate table WT move relative to the liquid confinement structure,care must be taken to ensure that the seal formed by a meniscus ofliquid between the liquid confinement structure and the substrate Wand/or substrate table WT does not break down. The introduction of astep on the surface may reduce the critical speed between the liquidconfinement structure and the substrate W and/or substrate table WT upto which the liquid confinement structure and/or the substrateW/substrate table WT may move without the seal, for example themeniscus, breaking down.

One or more of the edges 25 c, 25 d of the cover 25 may be configured toprovide a reduced step. For example, as discussed above, the thicknessof the cover may be locally reduced at one or more of the edges. Forexample, one or more of the edges 25 c, 25 d of the cover may beconfigured to have a profile as schematically depicted in any one ofFIGS. 22 to 25.

As depicted in FIG. 22, an edge of the cover 25 may be configured tohave a section 143 in which the cover 25 tapers to a point. Accordingly,such a cover may have no step. However, the extreme edge of the cover 25may be susceptible to damage.

In an alternative arrangement, as depicted in FIG. 23, the cover 25 mayhave an edge section 145 that includes a step 146 that is smaller thanthe thickness of the cover 25 and a tapered section between the step 146and the main body of the cover 25 that has the full thickness. Forexample, the main body of the cover 25 may be 25 μm thick and the step146 may be 10 μm thick. Such an arrangement has a smaller step than acover that has a perpendicular edge 25 c, 25 d but may be lesssusceptible to edge damage than an arrangement as depicted in FIG. 22.

As depicted in FIGS. 22 and 23, the tapered section 143, 145 of the edgeof a cover 25 may be configured to linearly increase in thicknessrelative to the distance from the edge. However, this is not essential.As depicted in FIGS. 24 and 25, which correspond to FIGS. 22 and 23,respectively, the tapered sections 147, 148 may be curved instead. Thismay avoid the provision of sharp corners, for example between thetapered section and the remainder of the cover 25 or between the taperedsection and a reduced step at the edge of the cover 25. Such sharpcorners may be a source of instability in the seal, for example themeniscus, between the liquid confinement structure and the underlyingsurface. Accordingly, avoiding such sharp corners may reduce thelikelihood of droplets being lost from the meniscus, reducing possibledefectivity as discussed above.

As shown in FIGS. 22 to 25, the lower corner of the cover 25, namely thecorner that in use may be in contact with the upper surface of thesubstrate W and/or the substrate table WT, may be a relatively sharpcorner. This may provide a relatively good seal between the cover 25 andthe substrate W and/or substrate table WT. However, it should beappreciated that the lower corner may be curved instead. This may reducethe likelihood of damage to the substrate W.

In general avoiding sharp corners on the cover may facilitate theprovision of a coating on the cover 25, if desired.

It should be appreciated that, although FIGS. 22 to 25 depict one edgeof a cover 25 with a tapered section and/or a rounded, one or more theedges of the cover 25 may be tapered and/or have one or more roundedcorners as discussed above. Furthermore, the edges of a cover 25 mayhave a different respective arrangements of a tapered section and/orrounded corners.

A further issue that may affect the selection of the arrangement of oneor both of the edges 25 c, 25 d of the cover 25 is the behavior of theimmersion liquid when the liquid confinement structure 12 crosses thecover 25. This behavior may also be affected by the configuration of theliquid confinement structure 12 and one or more materials used for thesubstrate table WT and the cover 25.

For example, when using a liquid confinement structure that does notinclude a gas knife and a lyophilic (e.g., hydrophilic) substrate tableWT and cover 25, liquid film pulling may be present. Liquid film pullingmay also occur in other arrangements. Liquid film pulling may lead toliquid loss on the substrate, which is undesirable. In particular, suchlost droplets may subsequently collide with the meniscus during furtherrelative movement between the liquid confinement structure 12 and thesubstrate table WT. These collisions may result in the formation ofbubbles in the immersion liquid.

The liquid film pulling may be caused by the movement of the edge of thecover 25 under the meniscus (or vice versa). When a meniscus crossesover a 90° height step, the meniscus velocity would have to be infiniteduring the step. Such a step occurs at a perpendicular edge 25 c, 25 dof a cover 25 such as shown in FIG. 21. Infinite meniscus velocity isnot actually possible so the meniscus is stretched, resulting in liquidfilm pulling as depicted in FIG. 33. Subsequently, the liquid film 201will break up, resulting in liquid loss on the substrate W and/orsubstrate table WT.

The liquid film pulling may be reduced by use of a tapered edge, forexample as depicted in FIG. 22. However, although the liquid film isdepinned earlier than in the case of a perpendicular edge, a liquid filmmay still be pulled. Accordingly, although liquid loss on the substrateand/or substrate table may be reduced, it may remain above a desiredlevel. This may be because it is not possible to form an infinitelysharp tip at the edge of the cover 25. Therefore, there may remain asmall edge that is effectively perpendicular at the end of the tip ofthe edge of the cover 25.

In an embodiment, an immersion liquid film disruptor is provided tostimulate fast break up of the liquid film. This may reduce the liquidloss.

In an embodiment, the immersion liquid film disruptor includes theprovision of a tapered edge on the cover 25 that is specificallyselected in order to reduce or minimize liquid film pulling.

FIG. 37 schematically depicts the shape of a meniscus of the immersionliquid crossing the cover 25 (e.g., when the cover 25 moves relative toand under the meniscus). The meniscus profile 251, 252, 253 is depictedat three successive times. The first meniscus profile 251 is depicted ata point in time when the meniscus is in contact with a non-taperedportion of the cover 25. A second meniscus profile 252 is shown at thepoint in time at which the meniscus is in contact with a tapered section143 of the edge of the cover 25. A third meniscus profile 253 depictsthe meniscus at a third time point when it is in contact with the uppersurface of the substrate W (in this case) and/or substrate table WT.

For each meniscus profile 251, 252, 253, FIG. 37 also depicts arespective dynamic contact angle 261, 262, 263, namely the angle of themeniscus profile 251, 252, 253 relative to a surface at the point atwhich it contacts the surface at a given velocity.

It will be appreciated that the dynamic contact angles 261, 263 of themeniscus in contact with the upper surface of the cover 25 in anon-tapered section and the upper surface of the substrate W/substratetable WT will be determined by the velocity of the substrate table WT(and therefore the cover 25 and the substrate W) relative to the liquidconfinement structure 12 and the properties of the surface of the cover25, the substrate W/substrate table WT, and the liquid.

As the meniscus traverses the tapered section 143 of the edge of thecover 25, the effective speed of the meniscus over the surfaceincreases. This effective speed is dependent on the angle 260 of thesurface of the tapered section 143 of the edge of the cover 25 relativeto the upper surface of the substrate W. The greater the angle 260, thegreater the effective velocity until, as discussed above, if the angleis 90°, the meniscus velocity would in theory be infinite (although inpractice this does not happen and the meniscus stretches, resulting inliquid film pulling).

FIG. 38 depicts a meniscus profile 254 in a specific situation in whichthe speed of the substrate table WT (and therefore the substrate W andthe cover 25) relative to the liquid confinement structure 12 is suchthat the dynamic contact angle 264 of the meniscus relative to thesurface of the tapered section 143 of the edge of the cover 25 is thesame as the angle 260 of the surface of the tapered section 143 relativeto the upper surface of the substrate W. Consequently, as shown, thesection 254 a of the meniscus profile 254 adjacent the edge of the cover25 is approximately parallel to the upper surface of the substrate W. Insuch a situation, when the meniscus approaches the extreme edge of thetapered section 143 of the edge of the cover 25, an elongate section 254a of the meniscus profile 254 may approach the upper surface of thesubstrate W simultaneously, resulting in the formation of a film ofliquid. This liquid film may subsequently break up, resulting in liquidloss on the substrate W and/or substrate table WT (where the taperedsection is on the substrate table WT side).

It will be appreciated that the situation depicted in FIG. 38 may occuras a result of the combination of the speed of the substrate table WTrelative to the liquid confinement structure 12, the nature of thematerial on the upper surface of the cover 25 (for example whether ornot it is lyophobic) and the angle 260 of the tapered section 143 of theedge of the cover 25.

In an embodiment, the angle 260 of the tapered section 143 of the edgeof the cover 25 may be selected in order to help ensure that, in use,the dynamic contact angle 262 of the meniscus as it crosses the taperedsection 143 of the edge of the cover 25 remains larger than the angle260 of the upper surface of the tapered section 143 of the edge of thecover 25 relative to the upper surface of the substrate W.

This angle may be determined by performing appropriate experiments inorder to identify the impact on the dynamic contact angle 262 ofvariations of the angle 260 of the upper surface of the tapered section143 of the edge of the cover 25 for different velocities of thesubstrate table WT relative to the liquid confinement structure 12.Experiments may also be performed in order to determine the effect ofvariations in the extent to which the upper surface of the cover 25 islyophobic for the immersion liquid to be used, namely for variations ofthe static contact angle. Such variations may be taken into account whenselecting the angle 260 of the tapered section 143 of the edge of thecover 25 to be used.

The appropriate angle 260 of the upper surface of the tapered section143 of the edge of the cover 25 may be specifically selected for acombination of a desired velocity of the substrate table WT, to be usedin operation of the lithographic apparatus when the meniscus crosses thecover 25, and a particular surface material of the cover 25. For examplethe surface material of the cover may be a material selected to form acoating 142 on the upper surface of the cover 25, as discussed above.

In particular, this may reduce the likelihood of pinning of the meniscusat the edge of the cover 25. In turn, this may reduce the likelihood offormation of a liquid film, which may break up and result in liquid losson the substrate W/substrate table WT, as discussed above.

In an embodiment of the present invention, it may be desirable to ensurethat, in use, the dynamic contact angle 262 of the meniscus profile 252at the point when the meniscus traverses the tapered section 143 of theedge of the cover 25 is such that this dynamic contact angle 262, lessthe angle 260 of the upper surface of the tapered section 143 of theedge of the cover 25, is greater than the dynamic contact angle 263 ofthe meniscus profile 253 when the meniscus is in contact with the uppersurface of the substrate W/substrate table WT. In other words thedifference between the dynamic contact angle 262 and the angle 260 ofthe upper surface of the tapered section 143 is greater than the dynamiccontact angle 263 of the meniscus profile 253 when the meniscus is incontact with the upper surface of the substrate W/substrate table WT.This may reduce the likelihood of pinning of the meniscus at the edge ofthe cover 25. In turn, this may reduce the likelihood of formation of aliquid film, which may break up and result in liquid loss on thesubstrate W/substrate table WT, as discussed above.

In an embodiment, an appropriate angle 260 of the upper surface of thetapered section 143 of the edge of the cover 25 may be selected takinginto account the dynamic contact angle 263 of the meniscus profile 253when the meniscus is in contact with the upper surface of the substrateW/substrate table WT. It will be appreciated that this in turn may bedependent on the intended speed of the substrate table WT in use whenthe meniscus is crossing the substrate W/substrate table WT at alocation adjacent to the edge of the cover 25.

Where, for example, the velocity of the substrate table WT relative tothe liquid confinement structure 12 is approximately 0.5 m/s, the staticcontact angle of the upper surface of the cover 25 is approximately 90°and the static contact angle of the upper surface of the substrate isapproximately 70° or 80°, an angle 260 of the upper surface of thetapered section 143 of the edge of the cover 25 relative to the uppersurface of the substrate W may be in the range of from about 15° to 45°,from about 15° to 30°, or approximately 20°.

As above, the desired angle 260 of the upper surface of the taperedsection 143 of the edge of the cover 25 may depend on the nature of thesurface of the cover 25, in particular in the region of the taperedsection 143. In general, it is desirable that the upper surface belyophobic because this may increase the angle 260 of the upper surfaceof the tapered section 143 of the edge of the cover 25 that may bepermitted for a given acceptable level of liquid loss on the substrateW/substrate table WT. This is beneficial because reducing the angle 260below certain levels may make manufacture of the cover 25 difficult.Furthermore, reducing the angle 260 may result in a larger section ofthe edge of the cover 25 being sufficiently thin that it is easilydamaged.

However, formation of a cover 25 having a lyophobic upper surface mayhave additional problems. In particular, as discussed above, a lyophobiccoating 142 may be applied to the upper surface of the cover 25.However, such a coating may degrade in use such that the static contactangle of the immersion liquid on the upper surface decreases over time.

In an embodiment, the selection of the angle 260 of the upper surface ofthe tapered section 143 of the edge of the cover 25 may be selected totake into account the expected degradation of the upper surface of thecover 25 over an acceptable time period. Beyond this point, the staticcontact angle of the immersion liquid on the upper surface of the cover25 may decrease to such an extent that the angle 260 of the edge of thecover is not sufficiently small to prevent or sufficiently reducepinning of the meniscus at the edge of the cover 25. Consequently, atthis point, liquid loss on the substrate W/substrate table WT may exceedan acceptable limit. At this stage, it may be necessary to replace thecover 25.

In an embodiment, the immersion liquid film disruptor includes one ormore structures that may be applied onto the upper surface and/or edgeof the cover 25. This structure causes film instability, resulting infilm break up. Such a surface profile may be combined with a cover 25having a perpendicular edge or any arrangement of tapered edge, asdescribed above.

The structure applied to the upper surface and/or edge of the cover 25may be in the form of any kind of plural local variations of thesurface. For example, elongate features such as ridges and/or channelsmay be provided. The cross section of such ridges and/or channels may beany appropriate shape. Alternatively or additionally, relatively shortfeatures such as pimples and/or dimples may be provided. Such pimplesand/or dimples may have any appropriate shape.

FIG. 34 depicts an embodiment, in which a plurality of ridges 202 areprovided on the upper surface of the cover 25. As shown, such anarrangement promotes the break up of the liquid film 203. Such anarrangement may reduce the likelihood of the meniscus being pinned.

FIG. 35 depicts an embodiment, in which a plurality of channels 204 areprovided on the edge of the cover 25. As shown, such an arrangementpromotes the break up of the liquid film 205. Such an arrangement mayreduce the likelihood of the meniscus being pinned.

In an embodiment, depicted in FIG. 36, the immersion liquid filmdisruptor includes a plurality of discrete gas jets 210 provided by theliquid confinement structure 12. The gas jets 210 are directed onto theliquid film as it starts to form, promoting fast break up of the film212. Such an arrangement may reduce the likelihood of the meniscus beingpinned.

The gas jets 210 may be provided, for example, by a row of aperturesformed in the surface of the liquid confinement structure 12 andconnected to a gas supply. The apertures may be provided outward of aline of openings 211 that are formed in the surface of the liquidconfinement structure and used to extract immersion liquid in order tocontain the immersion liquid. In other words, the apertures providingthe gas jets 210 may be on the opposite side of a line of openings 211to the space in which the immersion liquid is contained.

An advantage of using a plurality of discrete gas jets 210, rather thana gas knife for example, is that liquid droplets may not be collectedbetween a line of gas jets 210 and a line of openings 211. Collection ofliquid droplets in such an area may be a problem during movement of thesubstrate table WT relative to the liquid confinement structure. Forexample, liquid droplets collected in such an area during movement maycombine to form large droplets.

It will be appreciated that, in an embodiment, the immersion liquid filmdisruptor may include any combination of the above describedarrangements, an example of which is shown in FIG. 39.

In an embodiment, the upper surface 25 b of the cover 25 or the uppersurface 142 b of a coating 142 on the upper surface 25 b of the cover 25may be configured to be as flat as possible. This may further reduce anyinstabilities of the meniscus discussed above, reducing the likelihoodof droplets being lost from the meniscus and subsequent defects asdiscussed above.

In an embodiment, the cover may be a part of the substrate table. Anactuator system may be provided to move the cover between at leastclosed and open positions. In the closed position, the cover 25 may bein contact with the upper surface of a substrate W within the recess 22.In the closed position, the cover 25 may be in contact with the uppersurface 21 of the substrate table WT. In the closed position, the cover25 may cover the gap 23 between the edge of the substrate W and the edgeof the recess 22.

The cover 25 may be configured so that, as the gap passes underneath theimmersion space 11, with respect to the immersion liquid in the space,the gap is closed. By closing the gap, the stability of the meniscus incrossing the gap may be improved. In an embodiment, the cover forms aseal with one or both of the upper surface of a substrate W within therecess 22 and the upper surface 21 of the substrate table WT. A cover 25that provides a seal with both the upper surface of the substrate W andthe upper surface 21 of the substrate table WT may prevent immersionliquid from passing into the gap 23. The cover may reduce the inflow ofimmersion liquid into the gap 23. The cover may help reduce, if notprevent, the flow of bubbles into the space 11 as a consequence of thegap passing underneath the space 11.

In the open position, the cover 25 may be moved away from its locationat the closed position relative to the surface of the recess 22. When asubstrate is supported by the surface of the recess 22, the cover 25 maybe set apart from the substrate W. The open position may be arrangedsuch that, when the cover 25 is in the open position, the substrate Wmay be unloaded from the substrate table WT. If a substrate W is notpresent in the recess 22, a substrate W may be loaded onto the substratetable WT.

In an embodiment, the actuator system may be configured such that, inmoving the cover 25 from the closed position to the open position, itenlarges the open central section 26 of the cover 25, as depicted inFIG. 8. In such a process, the open central section 26 of the cover 25may be enlarged sufficiently that the open central section 26 is largerthan the upper surface of the substrate W in the open position. The opencentral section 26 of the cover 25 may be enlarged sufficiently for thesubstrate W to be able to pass through the central open section 26 ofthe cover 25.

In an embodiment, a substrate W may be loaded onto, or unloaded from, asubstrate table by moving the cover 25 to the open position and passingthe substrate W through the central open portion 26 of the cover 25. Inthe case of loading a substrate W to a substrate table WT, once thesubstrate W has passed through the open central section 26 of the cover25, the substrate W may be received in the recess 22 of the substratetable WT. Subsequently, the cover 25 may be moved by the actuator systemto the closed position, in which it covers the gap 23 between the edgeof the substrate W and the edge of the recess 22 in which the substrateW is supported.

The actuator system may be configured such that, in moving the cover 25to the open position, a plurality of portions of the cover 25 are movedin different respective directions relative to each other. Thisarrangement may be used in order to enlarge the open central section 26of the cover 25 in moving to the open position.

In an embodiment, the actuator system may be configured to elasticallydeform at least a part of the cover 25. For example, the actuator systemmay elastically deform at least part of the cover 25 when the actuatormoves the plurality of portions of the cover 25 in respective differentdirections in order to enlarge the open central section 26.

FIGS. 7 and 8 depict, in plan view, a cover 25 according to anembodiment of the invention in the closed and open positions,respectively. As shown, the cover 25 may be generally annular in shapein plan view. The inner periphery 31, e.g. circumference, of the cover25 may define the open central section 26 of the cover 25 when it is inthe closed position. A break in the generally annular shape of the cover25 may be provided between the inner periphery, e.g., circumference, 31and the outer periphery, e.g., circumference, 32 of the cover 25.

In an arrangement such as that depicted in FIGS. 7 and 8, the cover 25has a plurality of portions 35 each of which are moveable by theactuator system in respective different directions. In moving theplurality of portions 35 the open central section 26 of the cover 25 maybe enlarged or reduced. The plurality of portions may be combinedtogether to form a single integral cover. However, as depicted in FIG.8, the provision of the break 30 across the periphery, e.g.,circumference, of the cover 25 may facilitate the elastic deformation ofthe cover 25 in order to enlarge the central open section 26.

Although the arrangement of FIGS. 7 and 8 includes a break 30 from theinner periphery 31 to the outer periphery 32 of the cover 25, this isnot essential.

Additional breaks may be provided in order to facilitate theenlargement, e.g., by elastic deformation, of the cover 25 in order toenlarge the open central section 26 of the cover 25 according to thisaspect of the invention.

The provision of any of the covers disclosed herein may have a varietyof additional benefits for a substrate table within a lithographicapparatus in addition to the reduction of defects caused by bubblesand/or the reduction of bubbles, as described above.

The cleaning of the substrate table WT and the immersion system may bereduced. This, in turn, may reduce the down time of the lithographicapparatus.

A cover may reduce the transfer of contaminants from the upper surfaceof the substrate W to the lower surface of the substrate W. This mayreduce defects that may be introduced as a result of the so-called backside contamination.

The provision of a cover covering the gap between the edge of thesubstrate W and the edge of the recess 22 may enable the edge of thesubstrate W to traverse the projection system and immersion system at ahigher speed than is otherwise possible. This may increase thethroughput of the lithographic apparatus.

The provision of a cover may obviate the need for an extraction systemin order to remove immersion liquid and bubbles from the gap between theedge of the substrate W and the edge of the recess 22. This may reducethe heat load applied to the substrate table WT. The thermal stabilityof the substrate table WT may improve. The overlay accuracy of patternsformed on the substrate W may consequently improve.

An extraction system for the gap between the edge of the substrate W andthe edge of the recess 22 may be a two-phase extractor. This type ofextractor may produce flow induced vibrations. Therefore, the provisionof a cover, which may result in such an extractor being obsolete (notbeing required), may reduce the vibrations within the substrate tableWT.

The provision of a cover may result in a simpler system overall than asystem that uses an extractor for the gap between the edge of thesubstrate W and the edge of the recess 22, as disclosed above. Theprovision of a cover over the gap 23 may reduce the cost of goods of theapparatus as a whole.

It should be appreciated that the provision of a cover according to anaspect of the invention may eliminate the need for an extraction systemat the gap between the edge of the substrate W and the edge of therecess 22, as discussed above. However, a cover according to an aspectof the present invention may be used in conjunction with an extractionsystem. The benefits discussed above may still apply because therequirements of the extraction system may be reduced.

FIGS. 9 and 10 depict, in plan view, an arrangement of a cover 25according to an embodiment of the invention. The cover depicted in FIGS.9 and 10 is similar to the cover depicted in FIGS. 7 and 8 and, forbrevity, only the differences will be discussed in detail.

As shown, the cover 25 is formed from a plurality of discrete sections40. In the closed position, the sections 40 are arranged to abutadjacent sections 40 of the cover 25 in order to form a single cover 25.For example, as shown in FIG. 9, for a circular substrate W, when eachof the discrete sections 40 of the cover 25 abut each other in theclosed position, the combination of the discrete sections 40 provides acover 25 having a generally annular shape.

The actuator system is configured such that it can move portions of thecover 25 in different directions in order to move the cover from theclosed position to the open position. In the case of a cover 25 such asthat depicted in FIGS. 9 and 10, each such portion of the cover 25 isone of the discrete sections 40. The actuator system moves each of thediscrete sections 40 of the cover 25 in a respective differentdirection.

When the cover 25 is in the open position, the discrete sections 40 ofthe cover 25 may be set apart from each other, providing the enlargedopen central section 26 through which the substrate W may pass asdescribed above.

FIGS. 11, 12 and 13 depict, in cross-section, an actuator system thatmay be used in an aspect of the invention in, respectively, the closedposition, an intermediate position and the open position.

As shown FIG. 11, in the closed position, each portion of the cover 25is positioned on, and extends between, a peripheral portion 45 of theupper surface of the substrate W and the upper surface 21 of thesubstrate table WT. In moving the cover 25 from the closed position tothe open position, the actuator system 50 may be configured such thateach portion of the cover 25 is first moved in a direction substantiallyperpendicular to the upper surface of the substrate W and the uppersurface 21 of the substrate table WT.

FIG. 12 depicts a portion of the cover 25 in an intermediate positionbetween the closed and open positions after an initial movement, asdescribed above.

In moving from the open position to the closed position, the cover 25may be moved to the intermediate position shown in FIG. 12 such that thecover 25 may subsequently be moved to the closed position only by amovement in a direction substantially perpendicular to the upper surfaceof the substrate W and the upper surface 21 of the substrate table WT.

Such an arrangement may beneficially ensure that, when the cover 25 isin contact with the substrate W or close to the substrate W, therelative movement of the cover 25 to the substrate W is only in adirection that is substantially perpendicular to the upper surface ofthe substrate W. This may prevent or reduce the generation ofcontaminant particles at the edge of the substrate W. This may preventor reduce the movement of pre-existing contaminant particles at the edgeof the substrate W towards the upper surface of the substrate W on whicha pattern is to be formed. On contacting the substrate by moving thecover in a direction substantially perpendicular to the surface of thesubstrate W, a force applied to the substrate W is applied in adirection substantially perpendicular to the substrate W. As the forceis applied around the periphery of the substrate W, the force applied issubstantially uniform. Distortions in the substrate W caused by theapplication of the force are thereby reduced, if not minimized. Forcesin the plane of the substrate W by application of the cover 25 arereduced or minimized, limiting the movement of the substrate W in therecess. Position errors by applying the cover 25 to the edge of thesubstrate W may be reduced, if not prevented.

The actuator system 50 may be configured such that it can move each ofthe portions of the cover 25 between the intermediate position depictedin FIG. 12 and the open position depicted in FIG. 13 by moving each ofthe portions of the cover 25 in a direction that is substantiallyparallel to the upper surface of the substrate W and the upper surface21 of the substrate table WT.

As shown in FIGS. 11, 12 and 13, the actuator system 50 may include anactuator stage 51 that is configured to provide movement of the cover 25in a direction substantially perpendicular to the upper surface of thesubstrate W and the upper surface 21 of the substrate table WT, forexample in a vertical direction. The actuator stage 51 may be referredto as a transverse actuator stage.

The actuator system 50 may include an actuator stage 52 configured toprovide movement of the cover 25 in a direction substantially parallelto the upper surface of the substrate W and the upper surface 21 of thesubstrate table WT, for example in a horizontal direction. The actuatorstage 52 may be referred to as a lateral actuator stage. position.

It will be appreciated that, although the use of pneumatic actuators asdepicted may be beneficial, alternative actuators may be used for one orboth of the actuator stages 51, 52. For example, an electrostaticactuator and/or an electromagnetic actuator may be used.

The actuator stage 51 may be configured in order to ensure thatsubstantially the only movement provided is in the directionsubstantially perpendicular to the upper surface of the substrate W andthe upper surface 21 of the substrate table WT. The actuator stage 51may include one or more movement guides. The one or more movement guidesare configured to permit relative movement of the components of theactuator stage 51 in the direction substantially perpendicular to theupper surface of the substrate W and the upper surface 21 of thesubstrate table WT. However, the movement guide reduces or minimizes themovement of the component of the actuator stage 51 in a directionsubstantially parallel to the upper surface of the substrate W and theupper surface 21 of the substrate table WT.

FIGS. 14 and 15 depict, in cross-section, an arrangement of movementguides that may be used in order to help ensure that the actuator stage51 only provides movement in a particular direction. Such a directionmay be a direction substantially perpendicular to the upper surface ofthe substrate W and the upper surface 21 of the substrate table WT. FIG.14 depicts a movement guide 60 when the cover 25 is in the closedposition. FIG. 15 depicts the movement guide 60 when the cover 25 is inthe open position.

As shown, the actuator stage 51 includes first and second components61,62. The first and second components 61,62 may be moved relative toone another in the direction substantially perpendicular to the uppersurface of the substrate W and the upper surface 21 of the substratetable WT by means of the actuator provided as described above. Elastichinges 63 are provided between the first and second components 61,62 ofthe actuator stage 51. The elastic hinges permit movement of the firstand second components 61,62 in a direction substantially perpendicularto the upper surface of the substrate W and the upper surface 21 of thesubstrate table WT. The elastic hinges are configured to restrictmovement in a direction substantially perpendicular to this desireddirection of movement.

It will be appreciated that an alternative or additional movement guidemay be used. However, the use of one or more such elastic hinges asdescribed above may be beneficial because this form of movement guidedoes not have, or desirably minimizes, frictional forces. Frictionalforces may reduce the reproducibility of the force that is applied onthe upper surface of the substrate W when the cover 25 is moved to theclosed position.

FIGS. 16, 17 and 18 depict a further actuator system that may be usedwith an aspect of the present invention. FIG. 16 depicts the actuatorsystem 70 when the cover 25 is in the closed position. FIG. 17 depictsthe actuator system 70 in an intermediate position. FIG. 18 depicts theactuator system 70 when the cover 25 is in the open position.

The actuator system 70 depicted in FIGS. 16, 17 and 18 may provide asimpler actuation system than that depicted in FIGS. 11, 12 and 13.Separate actuator stages are not required. Instead, each portion of thecover 25 is connected to a piston 71 that is mounted within a system ofmovement guides 72,73 within the substrate table WT.

A movement guide 72 may, in cooperation with the piston 71, be used tomove the cover 25 from the closed position in a direction substantiallyperpendicular to the upper surface of the substrate W and the uppersurface 21 of the substrate table WT to the intermediate position. Amovement guide 73 may be arranged such that, in conjunction with thepiston 71, it moves the cover 25 in a direction substantially parallelto the upper surface of the substrate W and the upper surface 21 of thesubstrate table WT. In order to move the cover 25 between the closed andopen positions, the gas pressure on one or both sides of the piston 71may be changed by connecting one or both of the movement guides 72,73 toan appropriate under-pressure or over-pressure source 74,75.

The cover 25 may be configured such that in the closed position it notonly covers the gap 23 between the edge of the substrate W and the edgeof the recess 22 in the substrate table but it covers a further gap 77.For example, an additional gap may exist between the actuator system anda part of the substrate table further away from the substrate holdersuch as an additional component 78. The additional component 78 may be acomponent of a sensor system used in order to monitor the positionand/or displacement of the substrate table WT relative to the projectionsystem.

FIGS. 19 and 20 depict, in cross-section, an embodiment of the inventionin which a different arrangement of cover 125 is provided to cover thegap 23 between the edge of the substrate W and the edge of the recess 22in the substrate table WT in which the substrate W is supported. Inparticular, a cover 125 of an embodiment of the invention may beconfigured to be moved away from the substrate table WT to permitloading/unloading a substrate W to/from the recess 22 in the substratetable WT. In such an arrangement it is not necessary to enlarge an opencentral section of the cover 125 in moving the cover 125 to the openposition.

In common with the arrangements discussed above, the cover 125 isarranged in the form of a thin plate of material that surrounds the edgeof the substrate W. The cover 125 extends from a peripheral area 45 ofthe upper surface of the substrate W to the upper surface 21 of thesubstrate receiving section. Openings 127 for gas outlets may beprovided that are connected to an under-pressure source 128. Thepressure in a space on the lower side 125 a of the cover 125 may belower than the gas pressure on the upper side 125 b of the cover 125.The pressure difference may be used in order to secure the cover 125 andsubstantially prevent any movement of the cover 125 during use.

In order to prevent or reduce deformation of the cover 125, the covermay include one or more supports 126 that extend from the lower surface125 a of the cover 125 to the bottom of the recess 22 when the cover 125is located on top of a substrate W in the recess 22.

In order to move the cover 125 in order to permit loading and unloadingof a substrate W, a cover handling system 130 such as a robot arm may beprovided. The cover handling system 130 may be specifically configuredsuch that the movement of the cover 125 when the cover 125 is in contactwith the substrate W or close to the substrate W is only in a directionthat is substantially perpendicular to the upper surface of thesubstrate W and the upper surface 21 of the substrate table WT.

As discussed above, in embodiments of the invention, for example thosedepicted in FIGS. 11 to 18, an actuator system may be provided thatmoves the cover 25 from an open position, in which a substrate W may beloaded to the substrate table WT and/or a substrate W may be unloadedfrom a substrate WT, to a closed position, in which the cover 25 extendsfrom the upper surface 21 of the substrate table WT to the periphery ofthe substrate W. In the closed position, the cover 25 may be in physicalcontact with the peripheral section of the substrate W and the uppersurface 21 of the substrate table WT, in particular if the cover 25 isto form a seal. Such physical contact could result in damage of one ormore of the cover 25, the substrate W and/or the upper surface 21 of thesubstrate table WT. Accordingly, an appropriate control system for theactuator system may be provided.

In an embodiment of the invention, a controller is provided in order tocontrol the actuator system that positions the cover 25. In order tohelp ensure that the cover is accurately moved relative to the substrateW and/or substrate table WT, the controller may use data that representsthe height of the upper surface of at least the peripheral section ofthe substrate W relative to the upper surface 21 of the substrate tableWT (or vice versa). Such data may, for example, be previously acquiredin a metrology station, which may be part of the lithographic apparatusor part of a lithography system including the lithographic apparatus.

Based on the data representing the height of the upper surface of theperipheral section of the substrate W relative to the upper surface 21of the substrate table WT (or vice versa), the controller may determinethe position to which the cover 25 should be moved in order to provide adesired contact between the cover 25 and the upper surface of thesubstrate W and the upper surface 21 of the substrate table WT.

An appropriate feedback mechanism may be provided for the controller tocontrol the actuator system to move the cover 25 to the desired positiondetermined by the controller.

The controller may be configured, for example, to help ensure that theposition of the cover 25 in the closed position is sufficiently close toor in contact with the upper surface of the peripheral section of thesubstrate W to prevent, reduce or minimize leakage of the immersionliquid. Alternatively or additionally, the controller may be configuredto help ensure that, when the cover 25 is in the closed position, theforce exerted on the upper surface of the peripheral section of thesubstrate W by the lower surface of the cover 25 is within a givenrange. For example, it may be desirable to ensure that the force is lessthan a certain value in order to prevent or reduce the likelihood ofdamage to the substrate W. Alternatively or additionally, it may bedesirable to ensure that the force exerted on the upper surface of theperipheral section of the substrate W by the lower surface of the cover25 exceeds a certain value in order to ensure that sufficient contact ismade in order to control the leakage of immersion liquid below the cover25.

In an embodiment of the invention, the data representing the height ofthe upper surface of the peripheral section of the substrate W relativeto the upper surface 21 of the substrate table WT (or vice versa) mayprovide data for the relative height at a plurality of locations aroundthe peripheral section of the substrate W. From such data, thecontroller may be able to determine the desired position of respectiveportions of the cover 25 at a plurality of locations around the edge ofthe substrate W.

In an embodiment of the invention, the actuator system may becorrespondingly configured to be able to adjust the height of the cover25 independently at a plurality of locations around the cover 25. Insuch an arrangement, local variations of the height of the upper surfaceof the substrate W and/or substrate table WT may be taken into accountin controlling the positioning of the cover 25 in the closed position.This may in turn assist in preventing or reducing immersion liquidleakage and/or damage to the substrate W, the substrate table WT and/orthe cover 25.

As identified above, when the cover 25 is moved to the closed position,it may exert a force on the upper surface of the peripheral section ofthe substrate W. It should be appreciated that this force may be exertedregardless of the arrangement of the control system for the actuatorsystem used to move the cover 25. The force exerted on the substrate Wmay be sufficient to cause a movement of the upper surface of thesubstrate W, for example due to deformation of the substrate and/or dueto deformation of the support section of the substrate table WT thatsupports the substrate W. Such movement of the upper surface of thesubstrate W may be undesirable because it may result in errors in thepattern formed on the substrate W.

In an embodiment of the invention, the cover 25 may be provided with aregion that is relatively flexible, namely has a lower stiffness thanthe remainder of the cover. Such a relatively flexible section may beconfigured such that, when the cover 25 is moved to the closed position,any forces exerted on the cover and/or any inaccuracies in thepositioning of the cover relative to the substrate W and/or substratetable WT results in a deformation of the relatively flexible section ofthe cover rather than a deformation of the substrate W or the supportsection of the substrate table WT that supports the substrate.

FIGS. 26 to 30 depict schematically, in cross-section, arrangements ofcovers 25 of an embodiment of the present invention having relativelyflexible sections. As shown in FIGS. 26 to 28, a cover 25 may be formedfrom a single section of material and one or more relatively flexiblesections may be provided in which the thickness of the cover is reduced.For example, as depicted in FIG. 26, one or more of the edge sections161,162 of the cover 25 may have smaller thickness than the thickness ofthe remainder 163 of the main body of the cover 25. The sections 161,162of reduced thickness will accordingly be less stiff than the remainder163 of the main body of the cover 25.

The sections 161,162 of reduced thickness of the cover 25 may extendaround the cover 25, for example along the entirety of the inside and/oroutside edge of the cover 25. It will also be appreciated that in somearrangements, only one edge of the cover 25 will have a section ofreduced thickness in order to provide a relatively flexible section.

It will be appreciated that such arrangements may be combined withembodiments discussed above in which the edge of the cover 25 istapered. In this case, it will be appreciated that the edges 161 a, 162a of the reduced thickness sections 161, 162 may be tapered. Similarly,the edges of the covers depicted in FIGS. 27 to 32, described below maybe tapered. However, for brevity, this is not discussed in detail foreach embodiment discussed below.

As depicted in FIG. 27, a relatively flexible section of the cover 25may be provided by the formation of a groove 165 in the lower surface ofthe cover 25. The groove 165 results in an associated portion 166 of thecover 25 that has a reduced thickness and therefore reduced stiffness.It will be appreciated that the groove 165 may extend around the cover25. Accordingly, in use, the groove 165 may be positioned above the gapbetween the edge of the substrate W and the edge of the recess in thesubstrate table WT, extending around the full periphery of thesubstrate.

Although FIG. 27 depicts an arrangement in which a single groove 165 isprovided in the lower surface of the cover 25, it will be appreciatedthat a plurality of grooves may be provided in order to increase theflexibility of a section of the cover 25. However, in general, it isdesirable to retain sufficient sections of the main body of the cover 25with relatively high stiffness, namely sections of the cover having thefull thickness, in order to help ensure that the cover 25 does notdeform excessively in use.

As depicted in FIG. 28, the arrangements depicted in FIGS. 26 and 27 maybe combined. In other words, a cover 25 may have a section of reducedthickness 161,162 at one or more of the edges of the cover 25 and mayalso be provided with one or more grooves 165 on the lower surface ofthe cover 25.

In corresponding further arrangements, as depicted in FIGS. 29 to 31respectively, the main body of the cover 25 may be formed from a planarsection of material 170 attached to at least one support section ofmaterial 171. The combination of the planar section of material 170 andthe support section of material 171 provides sections of the main bodyof the cover 25 having full thickness and, accordingly, relatively highstiffness. Sections of the main body of the cover 25 that are formedfrom the planar material 170 that is not supported by support sectionsof material 171 provide sections of the cover 25 of reduced thickness161,162 that have relatively low stiffness. Likewise, gaps between twosupport sections of material 171 provide grooves 165 that providerelatively flexible sections of the cover 25.

Although not depicted in FIGS. 26 to 31, it will be appreciated that thecovers 25 of this aspect of the invention may include supports such asthose discussed above, including supports to connect the cover 25 to anactuator system.

FIG. 32 depicts an embodiment of the present invention, in which themain body of the cover 25 is supported by one or more supports 172. Asshown, the cover 25 has a reduced thickness section 161,162 at eitheredge of the cover 25, providing relatively flexible sections of thecover 25. In addition, grooves 165 are provided in the lower surface ofthe cover 25. The grooves 165 are positioned such that they each extendaround the cover 25 in a position between a respective edge of the cover25 and the position of the one or more supports 172. Accordingly, thegrooves 165 provide additional relatively flexible sections of the cover25. It will be appreciated that in variations of this arrangement, oneor more of the relatively flexible sections of the cover 25 may beomitted.

In an embodiment, there is provided a lithographic apparatus comprisinga substrate table having an upper surface and a recess in the uppersurface that is configured to receive and support a substrate; a fluidhandling structure configured to contain immersion fluid in a spaceadjacent to the upper surface of the substrate table and/or a substratelocated in the recess; a cover comprising a planar main body that, inuse, extends around a substrate from the upper surface to a peripheralsection of an upper major face of the substrate in order to cover a gapbetween an edge of the recess and an edge of the substrate; and animmersion fluid film disruptor, configured to disrupt the formation of afilm of immersion fluid between an edge of the cover and immersion fluidcontained by the fluid handling structure during movement of thesubstrate table relative to the fluid handling structure.

In an embodiment, the immersion fluid film disruptor comprises an edgeof the cover tapered such that the thickness of the cover graduallydecreases across the edge. In an embodiment, the angle of the surface ofthe section of the cover that is tapered, relative to the upper majorface of the substrate, is selected based on one or more selected fromthe following: intended speed of the substrate table in use relative tothe fluid handling structure when a meniscus of the fluid is over thecover, dynamic contact angle of the fluid on the cover at the intendedspeed, and/or the dynamic contact angle of the fluid on the substrate atthe intended speed. In an embodiment, the angle of the surface of thesection of the cover that is tapered, relative to the upper major faceof the substrate, is in the range of from about 15° to 45°. In anembodiment, the angle of the surface of the section of the cover that istapered, relative to the upper major face of the substrate, is such thatthe dynamic contact angle of the fluid on the section of the cover whena meniscus of the fluid crosses the section of the cover in use less theangle of the surface of the section of the cover is greater than thedynamic contact angle of the fluid on the substrate in use. In anembodiment, the immersion fluid film disruptor comprises a surfaceprofile formed on the edge, an upper surface of the cover, or both, thesurface profile having a plurality of local variations in the surface.In an embodiment, the local variations include ridges, channels,pimples, dimples and/or other protrusions or recesses. In an embodiment,the immersion fluid film disruptor comprises a plurality of discrete gasjets formed on a surface of the fluid handling structure opposite theupper surface of the substrate and/or substrate table. In an embodiment,the gas jets are each configured to provide a jet of gas onto the filmof immersion liquid as it forms. In an embodiment, the plurality of gasjets are provided by a corresponding plurality of apertures formed inthe surface of the fluid handling structure. In an embodiment, thesurface of the fluid handling structure comprises a line of openings,surrounding the space in which immersion fluid is contained, configuredto extract immersion fluid in order to contain the immersion fluid inthe space; and the plurality of gas jets are provided outwardly of theline of openings.

In an embodiment, there is provided a cover for use in an immersionlithographic apparatus that includes a substrate table having asubstantially planar upper surface in which is formed a recess that isconfigured to receive and support a substrate, the cover comprising asubstantially planar main body that, in use, extends around thesubstrate from the upper surface to a peripheral section of an uppermajor face of the substrate in order to cover a gap between an edge ofthe recess and an edge of the substrate, wherein the cover comprises animmersion fluid film disruptor configured to disrupt the formation of afilm of immersion fluid between the edge of the cover and immersionfluid contained by a fluid handling structure of the immersionlithographic apparatus during movement of the substrate table relativeto the fluid handling structure.

In an embodiment, there is provided a method of designing a cover foruse in an immersion lithographic apparatus that includes a substratetable having a substantially planar upper surface in which is formed arecess that is configured to receive and support a substrate, the covercomprising a substantially planar main body that, in use extends aroundthe substrate from the upper surface to a peripheral section of an uppermajor face of the substrate in order to cover a gap between an edge ofthe recess and an edge of the substrate, wherein an edge of the cover istapered such that the thickness of the cover gradually decreases acrossthe edge; and the method comprises selecting the angle of the surface ofthe section of the cover that is tapered, relative to the upper majorface of the substrate, in order that the section of the cover in usedisrupts the formation of a film of immersion fluid between the edge ofthe cover and the immersion fluid contained by a fluid handlingstructure of the lithographic apparatus during movement of the substratetable relative to the fluid handling structure.

In an embodiment, the angle of the surface of the section of the coverthat is tapered, relative to the upper major face of the substrate, isselected based on one or more selected from the following: intendedspeed of the substrate table in use relative to the fluid handlingstructure when a meniscus of the fluid is over the cover, dynamiccontact angle of the fluid on the cover at the intended speed, anddynamic contact angle of the fluid on the substrate at the intendedspeed. In an embodiment, the method further comprises forming the coveraccording to the design.

In an embodiment, there is provided a cover for use in an immersionlithographic apparatus, manufactured according to a design provided by amethod of designing the cover for use in an immersion lithographicapparatus that includes a substrate table having a substantially planarupper surface in which is formed a recess that is configured to receiveand support a substrate, the cover comprising a substantially planarmain body that, in use extends around the substrate from the uppersurface to a peripheral section of an upper major face of the substratein order to cover a gap between an edge of the recess and an edge of thesubstrate, wherein an edge of the cover is tapered such that thethickness of the cover gradually decreases across the edge; and themethod comprising selecting the angle of the surface of the section ofthe cover that is tapered, relative to the upper major face of thesubstrate, in order that the section of the cover in use disrupts theformation of a film of immersion fluid between the edge of the cover andthe immersion fluid contained by a fluid handling structure of thelithographic apparatus during movement of the substrate table relativeto the fluid handling structure.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications in manufacturing components with microscale, or evennanoscale features, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may refer to a substrate thatalready contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

To operate one or more movements of a component of the presentinvention, such as an actuator, there may be one or controllers. Thecontrollers may have any suitable configuration for receiving,processing, and sending signals. For example, each controller mayinclude one or more processors for executing the computer programs thatinclude machine-readable instructions for the methods described above.The controllers may include data storage medium for storing suchcomputer programs, and/or hardware to receive such medium.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as explicitly described. For example, the embodiments of theinvention may take the form of a computer program containing one or moresequences of machine-readable instructions describing a method asdisclosed above, or a data storage medium (e.g. semiconductor memory,magnetic or optical disk) having such a computer program stored therein.Further, the machine readable instruction may be embodied in two or morecomputer programs. The two or more computer programs may be stored onone or more different memories and/or data storage media. The computerprograms may be suitable for controlling a controller referred toherein.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above, whether the immersion liquid is provided in the form ofa bath, only on a localized surface area of the substrate, or isunconfined on the substrate and/or substrate table. In an unconfinedarrangement, the immersion liquid may flow over the surface of thesubstrate and/or substrate table so that substantially the entireuncovered surface of the substrate table and/or substrate is wetted. Insuch an unconfined immersion system, the liquid supply system may notconfine the immersion liquid or it may provide a proportion of immersionliquid confinement, but not substantially complete confinement of theimmersion liquid.

A liquid supply system as contemplated herein should be broadlyconstrued. In certain embodiments, it may be a mechanism or combinationof structures that provides a liquid to a space between the projectionsystem and the substrate and/or substrate table. It may comprise acombination of one or more structures, one or more liquid inlets, one ormore gas inlets, one or more gas outlets, and/or one or more liquidoutlets that provide liquid to the space. In an embodiment, a surface ofthe space may be a portion of the substrate and/or substrate table, or asurface of the space may completely cover a surface of the substrateand/or substrate table, or the space may envelop the substrate and/orsubstrate table. The liquid supply system may optionally further includeone or more elements to control the position, quantity, quality, shape,flow rate or any other features of the liquid.

Moreover, although this invention has been disclosed in the context ofcertain embodiments and examples, it will be understood by those skilledin the art that the present invention extends beyond the specificallydisclosed embodiments to other alternative embodiments and/or uses ofthe invention and obvious modifications and equivalents thereof. Inaddition, while a number of variations of the invention have been shownand described in detail, other modifications, which are within the scopeof this invention, will be readily apparent to those of skill in the artbased upon this disclosure. For example, it is contemplated that variouscombination or sub-combinations of the specific features and aspects ofthe embodiments may be made and still fall within the scope of theinvention. Accordingly, it should be understood that various featuresand aspects of the disclosed embodiments can be combined with orsubstituted for one another in order to form varying modes of thedisclosed invention. Thus, it is intended that the scope of the presentinvention herein disclosed should not be limited by the particulardisclosed embodiments described above, but should be determined only bya fair reading of the claims that follow.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

The invention claimed is:
 1. A lithographic apparatus comprising: asubstrate table having a cavity configured to receive a substrate; afluid handling structure configured to contain immersion fluid in aspace adjacent to the substrate table and/or the substrate when locatedin the cavity; a structure of the substrate table located at an edge ofthe cavity, the structure having an upper surface with a peripheralboundary and comprising: a boundary profile formed in the peripheralboundary of the structure, the boundary profile comprising a pluralityof protrusions laterally extending from the peripheral boundary and/orrecesses laterally extending into the peripheral boundary, and/or asurface profile formed on the upper surface of the structure, thesurface profile comprising (a) a plurality of troughs along the edge ofthe cavity, or (b) a plurality of protrusions along the edge of thecavity, or both (a) and (b), wherein the boundary profile and/or surfaceprofile is configured to disrupt an immersion fluid film, or itsformation, between a part of the structure and the immersion fluidcontained by the fluid handling structure during movement of thesubstrate table relative to the fluid handling structure.
 2. Thelithographic apparatus of claim 1, wherein an edge of the structure atthe peripheral boundary is tapered such that the thickness of thestructure gradually decreases in a direction towards the center of thecavity and across the edge of the structure.
 3. The lithographicapparatus of claim 2, wherein the structure comprises the plurality oftroughs and/or protrusions of the surface profile and the troughs and/orprotrusions are formed in the tapered edge of the structure.
 4. Thelithographic apparatus of claim 1, wherein the structure comprises theplurality of troughs and/or protrusions of the surface profile.
 5. Thelithographic apparatus of claim 4, wherein the plurality of troughsand/or protrusions are arranged along an arc.
 6. The lithographicapparatus of claim 1, wherein at least part of the structure surroundsthe substrate when located on the substrate table.
 7. The lithographicapparatus of claim 1, wherein the structure comprises the protrusions ofthe surface profile.
 8. A lithographic apparatus comprising: a substratetable having a cavity configured to receive a substrate; a fluidhandling structure configured to contain immersion fluid in a spaceadjacent to the upper surface of the substrate table and/or thesubstrate when located in the cavity; and a structure of the substratetable, the structure having an upwardly-facing surface comprising aplurality of troughs and/or protrusions along the edge of the cavityand/or along an edge of the substrate when located in the cavity,wherein the troughs and/or protrusions are configured to disrupt animmersion fluid film, or its formation, between a part of the structureand the immersion fluid contained by the fluid handling structure duringmovement of the substrate table relative to the fluid handlingstructure.
 9. The lithographic apparatus of claim 8, wherein an edge ofthe structure is tapered such that the thickness of the structuregradually decreases in a direction towards the center of the cavity andacross the edge of the structure.
 10. The lithographic apparatus ofclaim 9, wherein the troughs and/or protrusions are formed in thetapered edge of the structure.
 11. The lithographic apparatus of claim8, wherein the plurality of troughs and/or protrusions are arrangedalong an arc.
 12. The lithographic apparatus of claim 8, wherein atleast part of the structure surrounds the substrate when located on thesubstrate table.
 13. The lithographic apparatus of claim 8, wherein thetroughs and/or protrusions having a direction of elongationperpendicular to the nearest portion of an edge of the structure. 14.The lithographic apparatus of claim 8, wherein the upwardly-facingsurface comprises the protrusions along the edge of the cavity and/oralong an edge of the substrate when located in the cavity.
 15. Alithographic apparatus comprising: a substrate table configured to holda substrate having a peripheral edge; a fluid handling structureconfigured to contain immersion fluid in a space adjacent to the uppersurface of the substrate table and/or the substrate when located in thecavity; and a ring structure having an inner peripheral edge conformingin shape with the peripheral edge of the substrate, the structure havingan upwardly-facing surface comprising a plurality of troughs and/orprotrusions along, and extending to, the edge of the structure, whereinthe troughs and/or protrusions are configured to disrupt an immersionfluid film, or its formation, between a part of the structure and theimmersion fluid contained by the fluid handling structure duringmovement of the substrate table relative to the fluid handlingstructure.
 16. The lithographic apparatus of claim 15, wherein the edgeof the structure is tapered such that the thickness of the structuregradually decreases in a direction towards the center of the ringstructure and across the edge of the structure.
 17. The lithographicapparatus of claim 16, wherein the troughs and/or protrusions are formedin the tapered edge of the structure.
 18. The lithographic apparatus ofclaim 15, wherein the plurality of troughs and/or protrusions arearranged along an arc.
 19. The lithographic apparatus of claim 15,wherein at least part of the structure surrounds the substrate whenlocated on the substrate table.
 20. The lithographic apparatus of claim15, wherein the upwardly-facing surface comprises the protrusions along,and extending to, the edge of the structure.